Motor drive device and electric equipment utilizing the same

Abstract

Brushless DC motor ( 4 ) is driven based on a first or second waveform signal output from switching determination unit ( 11 ), which switches outputting so that a first waveform signal by first waveform generation unit ( 6 ) is output when the speed of rotor ( 4 a ) is determined to be lower than a predetermined speed, and a second waveform signal by second waveform generation unit ( 10 ) is output when the speed of rotor ( 4 a ) is determined to be higher than the predetermined speed. Thereby, drive is stable even at high speed/under high load, and a driving range is extended.

1 . A motor drive device for driving a brushless DC motor comprising a rotor and a stator having three-phase windings, the motor drive device comprising:
 an inverter for supplying electric power to the three-phase windings;   a terminal voltage obtaining unit for obtaining a terminal voltage of the brushless DC motor;   a first waveform generation unit for outputting a first waveform signal that is a waveform having a conduction angle of 120° or more and 150° or less;   a frequency setting unit for setting a frequency by changing only the frequency while keeping a duty constant;   a second waveform generation unit for outputting a second waveform signal that is a waveform having a predetermined relation with respect to the terminal voltage obtained by the terminal voltage obtaining unit, the frequency set by the frequency setting unit, and a conduction angle of 120° or more and less than 180°;   a switching determination unit for switching output so that the first waveform signal is output when a speed of the rotor is determined to be lower than a predetermined speed, and the second waveform signal is output when the speed of the rotor is determined to be higher than the predetermined speed; and   a drive unit for outputting a drive signal to the inverter indicating a supplying timing of electric power supplied to the three-phase windings based on one of the first and the second waveform signals output from the switching determination unit.   
     
     
         2 . The motor drive device of  claim 1 ,
 further comprising a position detection unit for detecting a position of the rotor,   wherein the first waveform generation unit outputs the first waveform signal based on the position of the rotor output from the position detection unit.   
     
     
         3 . The motor drive device of  claim 2 ,
 wherein the position detection unit detects the position of the rotor by detecting a zero-crossing point of the terminal voltage obtained by the terminal voltage obtaining unit.   
     
     
         4 . The motor drive device of  claim 1 ,
 further comprising a frequency limiting unit receiving an input of the frequency set by the frequency setting unit, and for outputting the input frequency when the frequency is equal to or below an upper limit frequency and outputting the upper limit frequency when the frequency is above the upper limit frequency.   
     
     
         5 . The motor drive device of  claim 4 ,
 further comprising an upper limit frequency setting unit for setting the upper limit frequency based on a maximum frequency of the first waveform signal, and outputting it to the frequency limiting unit.   
     
     
         6 . The motor drive device of  claim 5 ,
 further comprising an upper limit frequency changing unit for resetting the upper limit frequency by temporally switching from drive by the second waveform signal to drive by the first waveform signal when a predetermined time has passed after the start of drive by the second waveform signal.   
     
     
         7 . The motor drive device of  claim 1 ,
 wherein the rotor of the brushless DC motor comprises a permanent magnet embedded in an iron core, and has saliency.   
     
     
         8 . The motor drive device of  claim 1 ,
 wherein the brushless DC motor drives a compressor.   
     
     
         9 . The motor drive device of  claim 8 ,
 wherein the compressor is a reciprocating compressor.   
     
     
         10 . The motor drive device of  claim 8 ,
 wherein a refrigerant used in the compressor is R600a.   
     
     
         11 . Electric equipment comprising a brushless DC motor driven by a motor drive device of  claim 1 .